/Engine/Source/Runtime/Experimental/Chaos/Public/GeometryCollection/GeometryCollectionClusteringUtility.h
Finds the root bone in the hierarchy, the one with an invalid parent bone index
static void GetRootBones ( const [FGeometryCollection](API\Runtime\Chaos\GeometryCollection\FGeometryCollection) * GeometryCollection, [TArray](API\Runtime\Core\Containers\TArray)< int32 > & RootBonesOut )